With the recent trend of miniaturizing semiconductor devices, various processing methods capable of achieving more miniaturized structures have been proposed. Among them, a method for forming a thin film on a semiconductor substrate by using an excited species formed from exciting gas has been has drawn attention.
For example, as a method for forming a high quality thin film on a substrate by supplying a processing gas to a heated substrate under a depressurized atmosphere, ALD (Atomic Layer Deposition) has drawn considerable attention. In ALD, various species of source gases are alternately supplied to a substrate in a depressurized atmosphere. Then the gases react on the heated substrate, thereby forming a very thin film of reaction product. Although setting the substrate at high temperature is effective in promoting the reaction of the source gases on the substrate, raising the heating temperature of the substrate has a limit. For example, for a silicon wafer for semiconductor, preferably the temperature of the substrate is set at 400° C. or less.
Meanwhile, to promote the reaction of the source gases on the substrate at relatively low temperature, one technology uses excited species by exciting source gases. Various methods exist for producing excited species, but a method for converting the source gas into plasma is commonly used.
Further, in the wiring process of a semiconductor integrated circuit, formation of a barrier film is necessary to suppress copper (Cu) film as a wiring material from diffusing into the low dielectric interlayer insulating film (low-K film). As for forming the barrier film, TiN film, TaN film, WN film, Ti film, Ta film etc., are considered promising materials. It has been proposed that the barrier films are formed by using a processing gas which has been converted into plasma (for example, see reference 7 and article 1, as listed below).
References related to the technical background of the present invention are as follows:    Reference 1: Japanese Patent Laid-open Application No. H06-89873;    Reference 2: Japanese Patent Laid-open Application No. H06-333875;    Reference 3: Japanese Patent Laid-open Application No. H07-252660;    Reference 4: U.S. Pat. No. 5,306,666;    Reference 5: U.S. Pat. No. 5,916,365;    Reference 6: U.S. Pat. No. 6,342,277;    Reference 7: U.S. Pat. No. 6,387,207; and    Article 1: S. M. Rossnagel, A. Sherman, F. Turner, “Plasma-enhanced atomic layer deposition of Ta and Ti for interconnect diffusion barriers”, J. Vac. Sci. Technol. July/August 2000, pp. 2016-2020
As an example method for forming Ti film by using a processing gas which has been converted into plasma, there is a method of using TiCl4 as source gas and H2 as reducing gas. In this method, Ti film is formed on a substrate, e.g., a wafer or the like, by alternately supplying H2 as reducing gas and TiCl4 as source gas, wherein reducing gas, H2, is excited by ICP (Inductively Coupled Plasma) to be converted into plasma. Such a method is referred to as the PE-ALD method.
As described above, in a processing apparatus for forming Ti film by using the PE-ALD (Plasma-Enhanced Atomic Layer Deposition) method, the supply of H2 is stopped while TiCl4 is supplied, to thereby switch the supply of H2 to TiCl4. For that reason, the operation of ICP, which is an excitation source, is stopped while H2 is not being supplied. In the PE-ALD method, since alternating supplies of TiCl4 and H2 are performed repeatedly over hundreds of times, ICP is stopped every time accordingly.
Here, if the operation of ICP is stopped and plasma is dissipated, to regenerate plasma for the next process, a time is necessary for plasma ignition. Further, once plasma has been ignited, more time is required for the plasma to reach a stable state. Therefore, every time the supplies of TiCl4 and H2 are alternated, it takes time to ignite and stabilize plasma, ultimately resulting in the problem of extending the overall processing time.